In the image, the face-on spiral galaxy NGC 6946 is ablaze with colorful galactic fireworks fueled by the births and deaths of multitudes of brilliant, massive stars. Astronomers suspect that massive stellar giants have been ending their lives in supernova explosions throughout NGC 6946 in rapid-fire fashion for tens of millions of years.

“In order to sustain this rate of supernova activity, massive, quickly evolving stars must form or be born at an equally rapid rate in NGC 6946,” said Gemini North Associate Director, Jean-René Roy. “Its stars are exploding like a string of firecrackers!”

Astronomers speculate that if just a million years of this galaxy’s history were compressed into a time-lapse movie lasting a few seconds, there would be nearly constant outbursts of light as new stars flare into view, while old ones expire in spectacular explosions. Over the past century, eight supernovae have exploded in the arms of this
stellar metropolis, occurring in 1917, 1939, 1948, 1968, 1969, 1980, 2002, and 2004. This makes NGC 6946 the most prolific known galaxy for supernovae during the past 100 years.

By comparison, the average rate for such catastrophic stellar outbursts in the Milky Way is about one per century, and only four have been recorded over the last thousand years. The last known supernova went off in our galaxy in the constellation Ophiuchus in 1604.

Yet, it is the ubiquitous occurrence of starbirth throughout NGC 6946 and not its supernovae that lend this galaxy its blazingly colorful appearance. For reasons not completely understood, it experiences a much higher rate of star formation than all the large galaxies in our local neighborhood. The prodigious output of stellar nurseries in this galactic neighbor eventually leads to accelerated numbers of supernova explosions.

Starbirth regions exist in most galaxies, particularly in spirals, and are obvious as clouds of
predominantly hydrogen gas called H II regions. These areas coalesce over millions of years to form stars. Young, hot, massive stars formed in these regions emit copious amounts of ultraviolet radiation, which strip the electrons from hydrogen atoms in which they are embedded. When these ionized hydrogen atoms re-associate with electrons they radiate in a deep red color (at a wavelength of 656.3 nanometers) as the electrons transition back to lower energy levels.

This Gemini image of NGC 6946 utilizes a selective filter specifically designed to detect the radiation emanating from the starbirth regions. Additional filters help to distinguish other details in the galaxy, including clusters of massive blue stars, dust lanes, and a yellowish core where older more evolved stars dominate.

NGC 6946 lies between 10 and 20 million light-years away on the border between the constellations of Cepheus and Cygnus, and was discovered by Sir William Herschel (1738-1822) on September
9, 1798. It continues to fascinate astronomers, who estimate that it contains about half as many stars as the Milky Way. They often use it to study and characterize the evolution of massive stars and the properties of interstellar gas. As viewed in the new Gemini optical image, we see only the “tip of the iceberg” of this galaxy. Its optical angular diameter is about 13 arcminutes, but viewed at radio wavelength at the frequency of neutral hydrogen (1420 Mhz or 21-cm line), it extends considerably more than the angular diameter of the Moon.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.